The Otus/Elmore rule: When adding something new to the campaign, try and imagine how Erol Otus would depict it. If you can, that's far enough...it's a good idea. If you can picture a Larry Elmore version...it's far too mundane and boring, excise immediately.

(The link above goes directly to Kellri's post, not the first post in the discussion.)

This is a marvelously succinct and apt way of addressing the question... if you're familiar with old-school (Advanced) Dungeons & Dragons. What are some other ways of phrasing this, for people who aren't familiar with those defining D&D artists?

One thing I immediately thought of was the Muppet Show's dramatization of Lewis Carroll's "Jabberwocky". At the end of the linked clip, Scooter comments, "I tell you, this is the weirdest thing we've ever done on this show!" Unfortunately the clip is missing Kermit's introduction of the sketch, which Scooter interrupts with this exchange: "Kermit, have you seen the set? It's really weird!" "Of course it's weird, Scooter, we're the Muppets." "No, I mean it's really weird!" My personal variant of the rule, then, would be, 'if the Muppets would describe it as weird, it's sufficiently weird.' However, the Muppet Show is 30 years old now (yikes) and so arguably as much out of date a reference as Erol Otus is.